The present invention relates to a particulate incinerating method and mechanism for use in a reverse-cleaning regenerative exhaust black smoke removing system for diesel engines. More particularly, the present invention relates to a particulate incinerating method and mechanism wherein the power consumption is minimal and a heater for ignition has a long lifetime.
There have been proposed various exhaust black smoke removing systems using a gas-permeable porous filter for trapping and incinerating particulates (soot) in exhaust gas discharged from diesel engines. FIG. 1 is a schematic view for describing the principle of a cross-flow filter for trapping particulates in exhaust gas. The cross-flow filter is known, for example, from JP-B2-5-63604 (Japanese Patent Publication No. 5-63604).
The cross-flow filter as shown in FIG. 1 has a filter consisting essentially of a multiplicity of rectangular filter plates 11 made of a gas-permeable porous ceramic material having a filter function, which are stacked in a rectangular parallelepiped configuration. Each filter plate 11 has a first passage 14 formed from a large number of through-holes 15, both ends of which are open. Each pair of adjacent filter plates 11 are separated from each other by spacers 22 to define a thin rectangular parallelepiped-shaped second passage 24 between the two filter plates 11.
Exhaust gas containing particulates, which is discharged from a diesel engine, is introduced into the first passages 14 from openings provided in inlet surfaces 12, as shown by the arrow E in FIG. 1. The exhaust gas is prevented from flowing out from particulate discharge surfaces 13. Consequently, the exhaust gas passes through the gas-permeable porous ceramic material constituting the filter plates 11 and further passes through the second passages 24 to flow out from gas outlet surfaces 23. Particulates of large diameter in the exhaust gas cannot pass through the ceramic material; therefore, these particulates are deposited on the wall surfaces of the first passages 14 and thus removed from the exhaust gas, and only dedusted exhaust gas H is discharged from the gas outlet surfaces 23. After exhaust gas has been passed through the first and second passages 14 and 24 for a predetermined period of time, cleaning air is passed for a short period of time (momentarily) in a direction reverse to the flow direction of exhaust gas, that is, from the second passages 24 to the first passages 14 through the gas-permeable porous material, thereby removing the deposited particulates from the wall surfaces of the first passages 14, and thus regenerating the filter by reverse cleaning. The particulates removed from the wall surfaces drop through the first passages 14 by gravity, as shown by the arrow P in FIG. 1, and enter a hopper (not shown) under the particulate discharge surfaces 13. The particulates are incinerated in the hopper.
FIG. 2 is a plan view schematically showing a conventional exhaust black smoke removing system using the filter shown in FIG. 1. In the system shown in FIG. 2, dust-containing exhaust gas E discharged from a diesel engine G enters an inlet chamber 62 through an exhaust inlet pipe 57. In the inlet chamber 62, the exhaust gas E is guided to the inlet surface 12 of the filter 10 and passed through the filter 10 to remove particulates therefrom, thus becoming dedusted exhaust gas H, which is then discharged through an exhaust outlet pipe 58, an exhaust valve 92, etc.
In the conventional exhaust black smoke removing system shown in FIG. 2, reverse cleaning of the filter 10 is carried out under control of a controller C as follows: After dust-containing exhaust gas E has been passed through the filter 10 for a predetermined period of time, a solenoid valve 93 is opened to allow compressed air of 6-8 kg/cm.sup.2 to be supplied from an air tank S to an actuator 94, causing the actuator 94 to close an exhaust valve 92. At substantially the same time as the exhaust valve 92 is closed, a solenoid valve 84 provided in an air pipe 82 for providing communication between the air tank S and an air nozzle 75 opening into the exhaust outlet pipe 58 is opened for a short period of time to allow compressed air to be jetted into the exhaust outlet pipe 58 through the solenoid valve 84 and an air nozzle 75. The compressed air flows through a path reverse to that of exhaust gas. That is, the air passes through the second passages of the filter 10 and further passes through the gas-permeable porous material to enter the first passages, thereby removing deposited particulates from the peripheral wall surfaces of the first passages in cooperation with the effect of pressure waves produced from the air nozzle 75, and allowing the removed particulates to drop into a hopper 68 through the particulate discharge surface 13. Thus, the filter 10 is regenerated by reverse cleaning.
Particulates dropping into the hopper 68 are incinerated by heat from an ignition heater 66 provided in the hopper 68. The ignition heater 66 is heated by electric power supplied from a battery V. This type of exhaust black smoke removing system is known from JP-B2-5-63604 (Japanese Patent Publication No. 5-63604) and JP-U-5-58812 (Japanese Utility Model Public Disclosure No. 5-58812). In order to avoid interference with the overall discharge of exhaust gas from the diesel engine during the filter reverse cleaning process, there are provided two parallel systems each consisting essentially of the filter 10, the exhaust valve 92, the hopper 68, etc., and the two systems are alternately subjected to reverse cleaning process, thereby allowing either of the exhaust outlet pipes 58 to be open at all times.
In the conventional reverse-cleaning regenerative exhaust black smoke removing system shown in FIGS. 1 and 2. particulates are incinerated in a hopper disposed away from the filter. Therefor, the heat of incineration of particulates is not directly applied to the filter, and thus no heat load is imposed on the filter. Moreover, ash resulting from the incineration of particulates will not accumulate in the filter; this enables the filter lifetime to be increased. However, systems to be mounted on vehicle are generally demanded to save electric power and to reduce costs. Therefore, a relatively low-cost heater is used for ignition of particulates, and because the ignition heater is buried in particulates, it is likely to overheat. Accordingly, the lifetime of the heater is unfavorably short.